Lens is fast, light, small, built like military aperatus but mosyt important is tack sharp.

Cons:

Cheap looking and feeling hood

This is easily my favourite lens. I bought a 17-40L after using this lens because I was so impressed. For the money, it cannot be beat. This is my first forray into L glass and it got me hooked. I cant go back to consumer zooms now, IM now spoiled. Go rent one for a few days, you too will believe.

I bought a 70-200 F4 L and was amazed so bought this lens and I love it. Very sharp and contrasty. AF is accurate on my 30D/ I bought a Sigma 17-70mm before this lens and the 17-40 is superior by far. I had to apply quite a bit of USM to Sigma pics while its usually not required with the Canon lens. I do not miss the range between 40-70mm.

Poor image quality even stopped down, cheap construction, distortion is the worse I have seen.

Bought lens, tried for a month, bought L lens, compared the 2 and sold the 17-85 right away. Its not a very good lens, a cheap lens with IS tacked on. OK for newbies or for travel but there are better choices out there. Needs allot of USM to look good.